Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as cellular telephone technology is advanced, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
Cellular devices have radio frequency (RF) processing circuits and receive or transmit radio communications signals typically using modulation schemes. The typical cellular device may have multiple transmit and receive pathways from the antenna to a digital signal processor (DSP). In particular, each signal pathway may comprise a filter to help isolate the desired frequency band from extraneous electromagnetic signals, for example, noise and interference.
Nevertheless, as frequency bands change because of regulatory reasons, expansion, etc., it may be problematic to change the components of the cellular device to utilize the new bandwidth. For example, redesigning filters and power amplifiers to use the new bandwidth may incur greater complexity and cost. Another potential design hurdle encountered when expanding a cellular device's bandwidth is newly created self-interference. For example, the harmonic frequencies of the newly used bandwidth may create problems for other frequency bands used in the cellular device, thereby inhibiting their operation.